Transmit power control (TPC) is a technique used in uplinks to control transmission power by a mobile station such that intercell interference is reduced to a minimum necessary level while maintaining necessary quality in communication with a base station by controlling transmission power. In a 4-th generation mobile communication system called an LTE (Long Term Evolution)-Advanced system or the like whose standard is being established by 3GPP (The Third Generation Partnership Project), a technique called carrier aggregation (hereinafter referred to as CA) is employed to realize a wide band greater than 20 MHz. In the CA technique, one system band that supports LTE Rel. 8 is used as a component carrier (hereinafter referred to as CC), and communication is performed by simultaneously using a plurality of CCs. CA in an uplink is explained below for a case where transmission power is controlled independently for each of a plurality of CCs.
FIG. 8 is a block diagram of a transmission apparatus of a mobile station that performs transmission to a base station by using three CCs. Note that for simplicity of illustration, only blocks necessary in describing the background art are shown.
Each independent information data to be transmitted by each one of CCs is subjected to error correction encoding performed by respective encoders 1-1 to 1-3, and further subjected to a modulation process such as QPSK (Quaternary Phase Shift Keying), 16QAM (16-ary Quadrature Amplitude Modulation) or the like by modulation units 2-1 to 2-3. The modulated signals are respectively subjected to DFT (Discrete Fourier Transform, also called DFT Pre-Coding) performed by respective DFT units 3-1 to 3-3 thereby being converted into frequency-domain signals and then allocated to resource blocks (which are minimum units each including one or more subcarriers used by a mobile station in accessing a base station and which hereinafter will be referred to as RBs) to be used by resource mapping units 4-1 to 4-3.
In a case where RBs allocated by the resource mapping units 4-1 to 4-3 are contiguous, OFDM (Orthogonal Frequency Division Multiplexing) signal generation units 5-1 to 5-3 generate contiguous DFT-S-OFDM (Discrete Fourier Transform Spread Orthogonal Frequency Division Multiplexing) signals. However, in a case where the RBs allocated are not contiguous, clustered DFT-S-OFDM signals are generated. Therefore, the transmission apparatus illustrated in FIG. 8 is capable of operating switchably in two access modes, that is, a contiguous DFT-S-OFDM mode and a clustered DFT-S-OFDM mode. The transmission power control units 6-1 to 6-3 are capable of controlling transmission power individually for each CC. Note that each block is given a number in a range from 1 to 3 following a hyphen for convenience in describing communication using three CCs. An RF (Radio Frequency) unit 7 combines signals and up-converts the combined signals to a carrier frequency band. A control unit 8 controls transmission power control units 6-1 to 6-3. The transmission power control units control power according to one of methods described below.
The methods of controlling transmission power by the transmission power control units 6-1 to 6-3 are described below. Transmission power PPUSCH,c(i) of PUSCH (Physical Uplink Shared Channel which is a so-called physical channel for transmitting data) transmitted for each CC is given by formula (1). Note that the transmission power given by formula (1) is for a case where only PUSCH is transmitted in uplink (NPL 1).
                                              ⁢                  [                      Formula            ⁢                                                  ⁢            1                    ]                                                                                          P                          PUSCH              ,              c                                ⁡                      (            i            )                          =                  min          ⁢                      {                                                                                                                              P                                                  CMAX                          ,                          c                                                                    ⁡                                              (                        i                        )                                                              ,                                                                                                                                                                                                                        10                            ⁢                                                                                                                  ⁢                                                                                          log                                10                                                            ⁡                                                              (                                                                                                      M                                                                          PUSCH                                      ,                                      c                                                                                                        ⁡                                                                      (                                    i                                    )                                                                                                  )                                                                                                              +                                                                                    P                                                              O_PUSCH                                ,                                c                                                                                      ⁡                                                          (                              j                              )                                                                                +                                                                                                                    α                                c                                                            ⁡                                                              (                                j                                )                                                                                      ·                                                                                                                                                                                                                    PL                            c                                                    +                                                                                    Δ                                                              TF                                ,                                c                                                                                      ⁡                                                          (                              i                              )                                                                                +                                                                                    f                              c                                                        ⁡                                                          (                              i                              )                                                                                                                                                                                                }                                              (        1        )            
A function min returns a minimum element of arguments. Here, PCMAX,c(i) is maximum transmission power assignable by the mobile station to a c-th CC, c is a CC index, i is a subframe number of a subframe that transmits PUSCH to be controlled, MPUSCH,c(i) is a number of RBs in PUSCH. Furthermore, j has a different value depending on a scheduling method of a radio resource of PUSCH used by the mobile station, and more specifically, j=0 in a case where semi-persistent scheduling is used in which a radio resource is assigned periodically, while j=1 in a case where dynamic scheduling is used in which a radio resource is dynamically assigned. On the other hand, j=2 when used to transmit a random access preamble (a signal that is transmitted at first from a mobile station to a base station to establish a connection between the base station and the mobile station). PO_PUSCH,c(i) prescribes minimum power necessary in a reception apparatus, and is determined by the sum of PO_NOMINAL_PUSCH,c(j) notified from the base station and PO_UE_PUSCH,c).
αc(j) is a value notified from the base station to the mobile station. When j=0 or j=1, one value is selected from {0, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1}, while when j=2, 1 is given. PLc is a value of a transmission path loss (path loss) (which is also called a coupling loss and which may be a loss taking into account an antenna gain and the like) which is estimated by the mobile station using a reference signal transmitted in downlink and which is expressed in units of dB. ΔTF,c(i) is a value determined by a modulation method or a coding method used by the mobile station. fc(i) indicates that transmission power is controlled by a closed loop, and fc(i) is a TPC command notified from the base station (a control value of transmission power transmitted from the base station) used in transmission power control by the closed loop.
The value calculated by formula (1) gives transmission power that allows the base station to achieve a particular reception level when the mobile station transmits PUSCH using CCs specified by c. If this transmission power is less than maximum transmission power PCMAX,c(i) of PUSCH allowable in the mobile station, then the transmission is performed using this transmission power. If the above-described transmission power is larger than PCMAX,c(i), then the transmission is performed using PCMAX,c(i) as the transmission power.